Semiconductor device and method for manufacturing the same

ABSTRACT

In a semiconductor device having a metal wiring conductor connected to a contact hole formed through an interlayer insulator layer formed on a lower level circuit, a lower level tungsten film is deposited under a condition giving an excellent step coverage so as to fill the contact hole, and an upper level tungsten film is further deposited under a condition of forming a film having a stress smaller than that of the lower level tungsten film. The metal wiring conductor is formed of a double layer which is composed of the lower level tungsten film and the upper level tungsten film, and therefore, has a reduced stress in the whole of the film. Thus, there is obtained the tungsten film wiring conductor which fills the inside of the contact hole with no void and therefore has a high reliability, and which has a low film stress. In addition, the number of steps in the manufacturing process can be reduced.

This is a divisional application of application Ser. No. 08/610,349,filed on Mar. 4, 1996 U.S. Pat. No. 5,843,840.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a semiconductor device and a method formanufacturing the same, and more specifically to a semiconductor devicehaving a metal wiring layer and a method for manufacturing the same.

2. Description of related art

First, one example of the prior art will be described. As a technologyfor filling a connection hole such as a fine contact hole or a finevia-hole for interconnecting wiring conductors of different levels, ablanket tungsten chemical vapor deposition (blanket WCVD) has beenreduced into practice, which is excellent in step coverage and low inresistance. In this blanket WCVD method, after a blanket tungsten filmis formed, the blanket tungsten film is etched back by a dry etching sothat the tungsten film of only a plug is caused to remain, and then, afilm of a metal such as aluminum is formed thereon, and patterned toform a patterned wiring conductor.

Recently, a method has been proposed in which a wiring conductor itselfis formed of the tungsten film, in order to omit the step of etchingback the tungsten film. Now, this method will be described withreference to FIGS. 1A to 1D.

First, as shown in FIG. 1A, a silicon oxide film 2 is formed on siliconsubstrate 1, and a contact hole is formed in the silicon oxide film 2.An adhesion layer 3 is deposited in the contact hole by a sputtering.The adhesion layer 3 is suitable to be formed of a double layer ofcomposed of a titanium (Ti) film and a titanium nitride (TiN) film.Then, a tungsten film 4 is deposited by a chemical vapor deposition(CVD), as shown in FIG. 1B. Furthermore, a photoresist pattern 5 for apossible wiring conductor is formed by a lithography, as shown in FIG.1C. The tungsten film 4 is etched by a dry etching using the photoresistpattern 5 as a mask, so that a desired wiring conductor 6 is completedas shown in FIG. 1D.

Next, another example of the prior art will be described. In asemiconductor device having an upper level metal wiring conductor and alower level metal wiring conductor which are separated by an interlayerinsulator film such as a silicon oxide film but which are interconnectedthrough a contact hole formed by selectively etching the interlayerinsulator film, it was a conventional practice of forming the metalwiring layers by a relatively simple and inexpensive sputtering.However, because a diameter of the contact holes has become small withadvanced microminiaturization, a void occurs in the contact hole ifsputtering having a poor step coverage is used. A long term reliabilityof the wiring conductor is deteriorated because of the void. Therefore,the metal wiring conductors have been formed by a chemical vapordeposition having an excellent step coverage to prevent generation ofthe void. However, if the metal wiring conductors are formed by thechemical vapor deposition, it is disadvantageous because a silicon waferis bowed from internal stress of the metal film. This often results in asuction failure in a next step performed in the same apparatus or in avacuum suction robot feeding machine for feeding it to a next step.

In order to avoid the above problem, the conventional semiconductordevice was formed as follows: As shown in FIG. 2A, an silicon oxide film12 is formed on a silicon substrate 11 in which a desired circuit hasbeen already formed. Then, a contact hole 13 is formed by selectivelyetching the silicon oxide film 12, and a refractory metal layer 14 isdeposited on a surface including the contact hole 13, by a sputtering.

Thereafter, as shown in FIG. 2B, a tungsten film 15 is formed by achemical vapor deposition using WF₆ and H₂ as a raw material, under acondition realizing an excellent step coverage, namely, a reaction ratecontrolling condition such as a WF₆ flow rate of 50 sccm to 100 sccm anda deposition temperature of 400° C. to 460° C.

Then, as shown in FIG. 2C, the tungsten film 15 is etched back so thatthe tungsten film 15 remains only in the inside of the contact hole 13but the tungsten film 15 is completely removed from the upper surface ofthe refractory metal film 14 so as to expose the surface of therefractory metal film 14.

Furthermore, as shown in FIG. 2D, an aluminum layer 17 is deposited by asputtering, and then, is patterned to form a wiring conductor composedof the refractory metal film 14 and the aluminum wiring layer 17 whichare connected to a lower level circuit in the contact hole 13.

In the first example of the prior art as mentioned above, the tungstenfilm formed by the blanket WCVD is required to fill a fine contact holehaving a diameter of not greater than 0.5 μm without occurrence of thevoid, and also to have a property which causes no problem in a processafter the tungsten film deposition step. In the prior art, however, thetungsten film used for forming a tungsten plug can fill the fine contacthole with no void, but has the internal stress of 1×10¹⁰ dyne/cm² ormore, so that the wafer has a large bowing. Therefore, if the wiringconductors were formed of the tungsten film used for forming thetungsten plug, a problem is encountered in which, a feed trouble occursin a feeding system of a semiconductor manufacturing machine for feedingit to a process after the tungsten film deposition step, particularly, alithography step for forming the wiring pattern.

In order to lower the stress of the tungsten film, it is a generalpractice to form a film deposition under a supply rate controllingcondition by lowering the WF₆ flow rate and/or by elevating thedeposition or growth temperature.

As shown in FIGS. 3A and 3B, if the metal film were formed by changingthe CVD film deposition condition of a tungsten film 16 to a conditionfor forming a film having a low internal stress, namely, to a supplyrate controlling condition, the step coverage property is deteriorated,so that a void 18 occurs, and a problem such as a low long-termreliability of the wiring conductor and the others is generated.

As mentioned above, with the film deposition under the supply ratecontrolling condition, the step coverage of the tungsten filmdeteriorates, and it becomes difficult to fill a fine contact of notgreater than 0.5 μm without generation of void.

Because of the problems mentioned above, it was difficult to use thetungsten film for the wiring conductor having small contacts.

In the second example of the prior art as mentioned above of thesemiconductor device and the method for manufacturing the same, themanufacturing process becomes long and complicated, resulting in anincreased manufacturing cost. In addition, in order to shorten themanufacturing process, if the metal wiring conductor is formed of ametal film formed by only the CVD process, there occurs the abovementioned problem caused by the high stress.

Thomas E. Clark, et al, “High Pressure Blanket CVD Tungsten”, SolidState Technology Japanese Edition, December 1989, pages 33-41 disclosesa different WCVD process. However, the tungsten film formed in thisprocess has a high internal stress, and therefore, cannot be used as thewiring conductor.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide asemiconductor device and a method for manufacturing the same, which haveovercome the above mentioned defects of the conventional ones.

Another object of the present invention is to provide a semiconductordevice and a method for manufacturing the same, which have a tungstenplug and a tungsten wiring conductor, and which have a minimized waferbowing and an excellent step coverage.

Still another object of the present invention is to provide a method formanufacturing a semiconductor device, which has a reduced number ofmanufacturing steps.

The above and other objects of the present invention are achieved inaccordance with the present invention by a semiconductor device having asemiconductor substrate having a principal surface thereof, aninterlayer insulator film formed on the principal surface of thesemiconductor substrate, a contact hole formed through the interlayerinsulator film to reach the principal surface, and a metal wiringconductor filling the contact hole to reach the principal surface andextending on the interlayer insulator film, the metal wiring conductorbeing formed of a lower level metal film having an excellent stepcoverage to fill the contact hole with no void, and an upper level metalfilm formed on the lower level metal film, the upper level metal filmbeing formed of the same metal as that of the lower level metal film,and the upper level metal film having an internal stress smaller thanthat of the lower level metal film.

In one embodiment, the lower level metal film having an excellent stepcoverage has a film thickness not smaller than 40% of a diameter of thecontact hole, and the remainder of a desired thickness is constituted ofthe upper level metal film having the internal stress smaller than thatof the lower level metal film.

According to another aspect of the present invention, there is provideda method for forming a semiconductor device having a wiring conductorformed of tungsten, the method including the steps of forming a tungstenfilm by a low pressure chemical vapor deposition, injecting ions intothe tungsten film, and patterning the ion-injected tungsten film so asto form a wiring conductor composed of the ion-injected tungsten film.

Preferably, the above method further includes the step of heat treatingthe ion-injected tungsten film before the patterning step. Furthermore,an internal stress of the tungsten film is reduced to a value notgreater than 8×10⁹ dyne/cm² by the ion injection and the heat treatmentor only by the ion injection.

According to still another aspect of the present invention, there isprovided a method for forming a semiconductor device having asemiconductor substrate a principal surface thereof, an interlayerinsulator film formed on the principal surface of the semiconductorsubstrate, a contact hole formed through the interlayer insulator filmto reach the principal surface, and a metal wiring conductor filling thecontact hole to connect with the principal surface and extending on theinterlayer insulator film, the method including the step of forming alower level metal film having an excellent step coverage on theinterlayer insulator film including an inside of the contact hole, andthe step of forming on the lower level metal film an upper level metalfilm having an internal stress smaller than that of the lower levelmetal film.

Preferably, the lower level metal film having an excellent step coveragehas a film thickness not smaller than 40% of a diameter of the contacthole, and the remainder of a desired thickness is constituted of theupper level metal film having the internal stress smaller than that ofthe lower level metal film.

In one embodiment, the lower level metal film and the upper level metalfilm are continuously formed.

In one preferred embodiment, the lower level metal film is formed by achemical vapor deposition under a reaction rate controlling condition,and the upper level metal film is formed by a chemical vapor depositionunder a supply rate controlling condition.

Specifically, the lower level metal film and the upper level metal filmare formed of tungsten by a chemical vapor deposition while maintaininga deposition temperature at a constant value within a range of 400° C.to 500° C., but the lower level metal film is formed by controlling aWF₆ flow rate on the order of 50 sccm to 100 sccm and the upper levelmetal film is formed by controlling a WF₆ flow rate on the order of 10sccm to 50 sccm.

Alternatively, the lower level metal film and the upper level metal filmare formed of tungsten by a chemical vapor deposition while maintaininga WF₆ flow rate at a constant value within a range of 10 sccm to 100sccm, but the lower level metal film is formed by controlling adeposition temperature on the order of 400° C. to 450° C., and the upperlevel metal film is formed by controlling a deposition temperature onthe order of 450° C. to 500° C.

As still another embodiment, the lower level metal film is formed oftungsten by a chemical vapor deposition by controlling a depositiontemperature on the order of 400° C. to 450° C. and by controlling a WF₆flow rate on the order of 50 sccm to 100 sccm, and the upper level metalfilm is formed of tungsten by a chemical vapor deposition by controllinga deposition temperature on the order of 450° C. to 500° C. and bycontrolling a WF₆ flow rate on the order of 10 sccm to 50 sccm.

Moreover, the lower level metal film and the upper level metal film arecontinuously formed so as to control a stress of the whole of the lowerand upper level metal film by changing a film thickness ratio betweenthe lower level metal film and the upper level metal film.

The above and other objects, features and advantages of the presentinvention will be apparent from the following description of preferredembodiments of the invention with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are diagrammatic sectional views of a semiconductordevice, for illustrating a conventionally proposed method of forming awiring conductor itself by the tungsten film, in order to omit the stepof etching back the tungsten film;

FIGS. 2A to 2D are diagrammatic sectional views of a semiconductordevice, for illustrating a different conventionally proposed method offorming a tungsten contact plug and a wiring conductor by an aluminum;

FIGS. 3A and 3B are diagrammatic sectional views of a semiconductordevice, for illustrating a conventionally proposed method of forming awiring conductor itself by the tungsten film, by changing the CVD filmdeposition condition of a tungsten film to a condition for forming afilm having a low internal stress;

FIGS. 4A to 4D are diagrammatic sectional views of a semiconductordevice, for illustrating a first embodiment of the process in accordancewith the present invention for manufacturing a semiconductor device;

FIG. 5 is a graph illustrating a WF₆ flow rate dependency of the stressand the step coverage of the tungsten film;

FIG. 6 is a graph illustrating a stress dependency of the feed troubleoccurrence percent in the semiconductor device manufacturing machine;

FIGS. 7A to 7D are diagrammatic sectional views of a semiconductordevice, for illustrating a second embodiment of the process inaccordance with the present invention for manufacturing a semiconductordevice;

FIGS. 8A to 8D are diagrammatic sectional views of a semiconductordevice, for illustrating third to sixth embodiments of the process inaccordance with the present invention for manufacturing a semiconductordevice;

FIG. 9 is a time chart illustrating the change of the WF₆ flow rate inthe third and fifth embodiments of the present invention;

FIG. 10A is a graph illustrating a temperature dependency of the stepcoverage and the film stress, in the CVD process for forming thetungsten film using WF₆ and H₂ as a raw material;

FIG. 10B is a graph illustrating a WF₆ flow rate dependency of the stepcoverage and the film stress, in the CVD process for forming thetungsten film using WF₆ and H₂ as a raw material;

FIG. 11 is a time chart illustrating the change of the film depositiontemperature in the fourth and fifth embodiments of the presentinvention;

FIG. 12 is a graph illustrating a relation between the stress of theoverall film and the ratio in film thickness between two films havingdifferent stresses; and

FIG. 13 is a graph illustrating a relation between the film stress andthe feed error percent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 4A to 4D, there are shown diagrammatic sectionalviews of a semiconductor device, for illustrating a first embodiment ofthe process in accordance with the present invention for manufacturing asemiconductor device.

As shown in FIG. 4A, after a silicon oxide film 2 having a thickness of1,000 Å to 10,000 Å is formed on a silicon substrate 1, a contact holeis formed through the silicon oxide film by use of a lithographytechnology and a dry etching technology, and then, an adhesion layer 3is formed in the contact hole by depositing a Ti film and a TiN film bysputtering. Each of the Ti film and the TiN film has a thickness on theorder of 500 Å to 2,000 Å. Thereafter, a tungsten film 4 having athickness of 3,000 Å to 7,000 Å is deposited on the adhesion layer 3 bya low pressure CVD process. At this time, the deposited tungsten film 4is required to fill the contact hole with no void. For this purpose, thedeposition condition is that the deposition temperature is on the orderof 425° C. to 475° C. and the WF₆ flow rate on the order of 50 cm³/minto 100 cm³/min or more. FIG. 5 is a graph illustrating a WF₆ flow ratedependency of the stress and the step coverage of the tungsten film. Ifthe tungsten film is deposited under a condition of forming a filmhaving an excellent step coverage, namely, under a reaction ratecontrolling condition, the stress of the deposited tungsten film is1.2×10¹⁰ dyne/cm² or more.

Thereafter, as shown in FIG. 4B, a material such as tungsten ormolybdenum is injected into the tungsten film 4 by means of an ionimplantation process. At this time, the condition for the ionimplantation is that an acceleration voltage is on the order of 100 KeVto 2,000 KeV and the dose is on the order of 1×10¹³ atoms/cm² to 5×10¹⁴atoms/cm². If the tungsten film 4 to be ion-implanted becomes thicker,it is preferred to perform the ion-implantation with a higher energy andwith a higher dose.

With the ion-implantation to the tungsten film 4, the stress of 1.2×10¹⁰dyne/cm² in the deposited tungsten film is reduced to the stress of8×10⁹ dyne/cm². As a result, there no longer occurs a problem, such as awafer feed error, in succeeding processes such as a lithography and adry etching which are performed after the completion of the tungstenfilm deposition.

Referring to FIG. 6, there is shown a graph illustrating a stressdependency of the feed trouble occurrence percent in the semiconductordevice manufacturing machine. It would be understood that the feedtrouble occurrence percent becomes zero according to the presentinvention.

Thereafter, as shown in FIG. 4C, a photo resist mask 5 is formed on thetungsten film 4 by use of a lithography technology, and then, as shownin FIG. 4D, the tungsten film 4 and the underlying adhesion layer 3 arepatterned by use of a dry etching technology so as to form a wiringconductor 6.

Thus, as mentioned above, it is possible to form a wiring conductorformed of a tungsten film used for filing a contact hole with anexcellent filling property having no void, by forming the tungsten filmby the CVD process and then by implanting ions into the tungsten film.

Now, a second embodiment of the present invention will be described withreference to FIGS. 7A to 7D, which are diagrammatic sectional views of asemiconductor device, for illustrating a second embodiment of theprocess in accordance with the present invention for manufacturing asemiconductor device.

First, similarly to the first embodiment, a silicon oxide film 2 isformed on a silicon substrate 1, and a contact hole is formed throughthe silicon oxide film by use of a lithography technology and a dryetching technology, and then, an adhesion layer 3 composed of a Ti filmand a TiN film is deposited by sputtering. Furthermore, a tungsten film4 is filled into the contact hole with no void by a CVD process, asshown in FIG. 7A.

Thereafter, as shown in FIG. 7B, silicon is injected into the tungstenfilm 4 by means of an ion implantation process. Further, a heattreatment is performed at 500° C. to 800° C. by use of a lamp annealleror in a diffusion furnace, as shown in FIG. 7C. With this heattreatment, the tungsten and the silicon react, with the result that thestress is further reduced. Thus, a heat-treated tungsten film 41 havinga reduced stress is formed.

Thereafter, similarly to the first embodiment and as shown in FIG. 7D, adesired wiring conductor 6 is formed by use of a lithography technologyand a dry etching technology.

As in the second embodiment, if ions such as silicon ions, which easilyreact with tungsten at a relatively low temperature, is injected intothe tungsten film, the injected ions react with the tungsten in thesucceeding heat treatment, with the result that the structure of thetungsten film changes and the stress is relaxed. Thus, the heat-treatedtungsten film 41 having a low stress can be formed.

In the above mentioned first and second embodiments, the stress of thewhole of the tungsten film is reduced. However, it is possible to reducethe stress in only a surface region of the tungsten film by changing theacceleration voltage and the dose of the ion implantation. In this case,the tungsten film has a double layer structure composed of a first layerportion formed by the CVD process and having a high stress, and a secondlayer portion having a stress reduced in accordance with the presentinvention. However, totally considering the whole of the tungsten filmof the double layer structure, the tungsten film has a reduced stress,and therefore, can be used as the tungsten film for the wiringconductor.

In addition, the material to be ion-implanted into the tungsten film canbe a refractory metal such as molybdenum or silicon, and furthermore,may be aluminum, phosphorus, boron, etc.

The heat treatment performed after the ion implantation in the secondembodiment can be performed in the case of the first embodiment and in acase of ion-implanting another material.

Now, a third embodiment of the present invention will be described withreference to FIGS. 8A to 8D, which are diagrammatic sectional views of asemiconductor device, for illustrating the third embodiment of theprocess in accordance with the present invention for manufacturing asemiconductor device. In addition, FIG. 9 is a time chart illustratingthe change of the WF₆ flow rate in the third embodiment of the presentinvention, and FIGS. 10A and 10B are graphs illustrating the grounds forthe condition of the third embodiment. FIG. 10 is a graph illustrating atemperature dependency of the step coverage and the film stress, in theCVD process for forming the tungsten film using WF₆ and H₂ as a rawmaterial, and FIG. 10B is a graph illustrating a WF₆ flow ratedependency of the step coverage and the film stress, in the CVD processfor forming the tungsten film using WF₆ and H₂ as a raw material.

As shown in FIG. 8A, a silicon oxide film 12 is formed on a siliconsubstrate 11 in which a desired circuit has been already formed, and thesilicon oxide film 12 is selectively etched to form a contact hole 13reaching a principal surface of the substrate 11.

Then, as shown in FIG. 8B, a refractory metal layer 14 is deposited onthe surface including the inside of the contact hole 13, by depositing atitanium film and a titanium nitride film by sputtering.

Thereafter, as shown in FIG. 8C, a tungsten film 15 is formed by achemical vapor deposition using WF₆ and H₂ as a raw material, under acondition realizing an excellent step coverage, namely, a reaction ratecontrolling condition such as a deposition temperature of 400° C. to450° C., a WF₆ flow rate of 50 sccm to 100 sccm and a H₂ flow rate of200 sccm to 3,000 sccm. At this time, the thickness of the depositedfilm 15 is controlled on such a degree as to fill the contact hole 13.For example, when the contact hole having a diameter of 0.5 μm, thethickness of the deposited film is 0.2 μm or more. In other words, thistungsten film 15 has a film thickness not smaller than 40% of a diameterof the contact hole.

Furthermore, as shown in FIG. 9, in the same deposition chamber, atungsten film 16 is continuously formed by the chemical vapor depositionusing WF₆ and H₂ as a raw material, under a condition for forming a filmhaving the stress lower than that of the tungsten film 15, namely, asupply rate controlling condition such as a WF₆ flow rate of 10 sccm to50 sccm but maintaining the deposition temperature as it is. Thus, ametal wiling film having a desired thickness as shown in FIG. 8D isformed.

Here, referring to FIGS. 10A and 10B, in the chemical vapor depositionusing WF₆ and H₂ as the raw material, the smaller the WF₆ flow rate is,and the higher the deposition temperature is, the smaller the internalstress of the deposited film becomes, and the worse the step coveragebecomes. Accordingly, if the tungsten films 15 and 16 are continuouslydeposited in the above mentioned order, it is possible to deposit themetal wiring film having less void and a low internal stress.

Next, a fourth embodiment of the present invention will be describedwith reference to FIGS. 8A to 8D and FIG. 11 which is a time chartillustrating the change of the film deposition temperature in the fourthembodiment of the present invention.

First, as shown in FIG. 8A, a silicon oxide film 12 is formed on asilicon substrate 11 in which a desired circuit has been already formed,and the silicon oxide film 12 is selectively etched to form a contacthole 13 reaching to a principal surface of the substrate 11. Then, asshown in FIG. 8B, a refractory metal layer 14 is deposited on thesurface including the inside of the contact hole 13, by a sputtering.

Thereafter, as shown in FIG. 8C, a tungsten film 15 is formed by achemical vapor deposition using WF₆ and H₂ as a raw material, under acondition realizing an excellent step coverage, namely, a reaction ratecontrolling condition such as a deposition temperature of 400° C. to450° C. and a WF₆ flow rate of 10 sccm to 100 sccm. At this time, thethickness of the deposited film is controlled on such a degree as tofill the contact hole 13. For example, when the contact hole having adiameter of 0.5 μm, the thickness of the deposited film is 0.2 μm ormore.

Furthermore, as shown in FIG. 11, in the same deposition chamber, atungsten film 16 is continuously formed by the chemical vapor depositionusing WF₆ and H₂ as a raw material, under a condition for forming a filmhaving the stress lower than that of the tungsten film 15, namely, asupply rate controlling condition such as a deposition temperature of450° C. to 500° C. but maintaining the WF₆ flow rate as it is. Thus, ametal wiring film having a desired thickness as shown in FIG. 8D isformed.

Further, a fifth embodiment of the present invention will be described.First, as shown in FIG. 8A, a silicon oxide film 12 is formed on asilicon substrate 11 in which a desired circuit has been already formed,and the silicon oxide film 12 is selectively etched to form a contacthole 13 reaching to a principal surface of the substrate 11. Then, asshown in FIG. 8B, a refractory metal layer 14 is deposited on thesurface including the inside of the contact hole 13, by a sputtering.

Thereafter, as shown in FIG. 8C, a tungsten film 15 is formed by achemical vapor deposition using WF₆ and H₂ as a raw material, under acondition realizing an excellent step coverage, namely, a reaction ratecontrolling condition such as a WF₆ flow rate of 50 sccm to 100 sccm anda deposition temperature of 400° C. to 450° C. At this time, thethickness of the deposited film is controlled on such a degree as tofill the contact hole 13. For example, when the contact hole having adiameter of 0.5 μm, the thickness of the deposited film is 0.2 μm ormore.

Furthermore, as shown in FIGS. 9 and 11, in the same deposition chamber,a tungsten film 16 is continuously formed by the chemical vapordeposition using WF₆ and H₂ as a raw material, under a condition forforming a film having the stress lower than that of the tungsten film15, for example a WF₆ flow rate of 10 sccm to 50 sccm and a depositiontemperature of 450° C. to 500° C. Thus, a metal wiring film having adesired thickness as shown in FIG. 8D is formed.

Now, a sixth embodiment of the present invention will be described withreference to FIGS. 12 and 13. FIG. 12 is a graph illustrating a relationbetween the stress of the overall film and the ratio in film thicknessbetween two films having different stresses, in the sixth embodiment,and FIG. 13 is a graph illustrating a relation between the film stressand the feed error percent, for the purpose of explaining the ground forgiving a target or desired film stress.

Similarly to the third embodiment, as shown in FIG. 8A, a silicon oxidefilm 12 is formed on a silicon substrate 11 in which a desired circuithas been already formed, and the silicon oxide film 12 is selectivelyetched to form a contact hole 13 reaching to a principal surface of thesubstrate 11. Then, as shown in FIG. 8B, a refractory metal layer 14 isdeposited on the surface including the inside of the contact hole 13, bya sputtering.

Thereafter, as shown in FIG. 8C, a lower level tungsten film 15 havingan excellent step coverage, similarly to the third and fourthembodiments, for example, having a stress of, 10E9 dyne/cm² to 15E9dyne/cm², and an upper level tungsten film 16 having the stress lowerthan that of the tungsten film 15, for example, having a stress of, 1E9dyne/cm² to 10E9 dyne/cm², are continuously deposited by a chemicalvapor deposition using WF₆ and H₂ as a raw material. Thus, a metalwiring film having a desired thickness as shown in FIG. 8D is formed.

Here, as shown in FIG. 12, it is possible to control the stress of thewhole of the combined tungsten films 15 and 16, by changing the filmthickness ratio between the tungsten film 15 and the tungsten film 16,namely, by changing the respective deposition times of the tungsten film15 and the tungsten film 16. For example, if the tungsten film 15 havinga stress of 10E9 dyne/cm² and the tungsten film 16 having a stress of5E9 dyne/cm² are combined, it is possible to obtain a desired stress inthe range of 5E9 dyne/cm² to 10E9 dyne/cm². Therefore, if it isnecessary to maintain the stress of the whole of the tungsten film at avalue not greater than 8E9 dyne/cm² (8×10⁹ dyne/cm²) as shown in FIG. 13for the purpose of avoiding the suction failure in the same chamber inthe steps after the tungsten film deposition step or in a vacuum suctiontype robot feeding for going to other succeeding steps, it is sufficientif the lower level tungsten film 15 is made not greater than 70% in thefilm thickness ratio.

In the above mentioned embodiment, the tungsten film 15 and the tungstenfilm 16 are continuously formed in the same chamber. However, thecontinuous formation is not indispensable. The tungsten film 15 and thetungsten film 16 can be formed in different chambers or in differentdeposition machines, or in the chemical vapor deposition and thesputtering, respectively.

As seen from the above, according to the present invention, it ispossible to form the tungsten film having an excellent filling propertyby use of the CVD process, and then to implant ions into the tungstenfilm so as to reduce the stress of the tungsten film. Thus, the tungstenfilm having the reduced stress can be used for forming the wiringconductor. As mentioned hereinbefore, the stress of the depositedtungsten film in accordance with the prior art was as high as 1.2×10¹⁰dyne/cm², and therefore, the wafer itself had a large bowing, so thatsuch a trouble had frequently occurred that the feeding of the waferstops in the feeding system of the semiconductor device manufacturingmachine. However, the present invention can eliminate this trouble inthe feeding system, and can form a patterned wiring conductor oftungsten without trouble.

Furthermore, since the present invention can reduce the stress of thetungsten film, it is possible to increase the film thickness of thetungsten film which is used as the wiring conductor.

In addition, as mentioned above, the present invention is characterizedin that, in a semiconductor device having a metal wiring film, when themetal wiring film is formed, the film deposition is carried out firstlyunder a condition for giving an excellent step coverage, and secondlyunder a condition for giving a low film stress. With thesecharacteristics, no void occurs in the contact, and therefore, along-term reliability of the wiring can be ensured. In addition, sincethe wiring structure having a low internal film stress can be obtained,the bowing of the wafer can be reduced, so that the feeding error insucceeding steps can be reduced.

Moreover, the etching back of the tungsten film 15 as shown in FIG. 2Cand the formation of the aluminum film 17 as shown in FIG. 2D, whichwere required in the prior art, can be omitted. Therefore, the number ofsteps can be reduced, and accordingly, the manufacturing cost can becorrespondingly reduced.

Additionally, by changing the film thickness ratio between two metalfilms having different stresses, it is possible to control the stress ofthe whole of the metal film to a desired value between the differentstresses of the two metal films.

The invention has thus been shown and described with reference to thespecific embodiments. However, it should be noted that the presentinvention is in no way limited to the details of the illustratedstructures but changes and modifications may be made within the scope ofthe appended claims.

What is claimed is:
 1. A method for forming a semiconductor devicehaving a semiconductor substrate a principal surface thereof, aninterlayer insulator film formed on said principal surface of saidsemiconductor substrate, a contact hole formed through said interlayerinsulator film to reach said principal surface, and a metal wiringconductor filling said contact hole to connect with said principalsurface and extending on said interlayer insulator film, the methodincluding the first step of forming a lower level metal film having anexcellent step coverage on said interlayer insulator film including aninside of said contact hole, and the second step of forming on saidlower level metal film an upper level metal film having an internalstress smaller than that of said lower level metal film.
 2. A methodclaimed in claim 1, wherein said lower level metal film having anexcellent step coverage has a film thickness not smaller than 40% of adiameter of said contact hole, and the remainder of a desired thicknessis constituted of said upper level metal film having the internal stresssmaller than that of said lower level metal film.
 3. A method claimed inclaim 1, wherein said lower level metal film and said upper level metalfilm are continuously formed.
 4. A method claimed in claim 1, whereinsaid lower level metal film is formed by a chemical vapor depositionunder a reaction rate controlling condition, and said upper level metalfilm is formed by a chemical vapor deposition under a supply ratecontrolling condition.
 5. A method claimed in claim 1, wherein saidlower level metal film and said upper level metal film are formed oftungsten by a chemical vapor deposition while maintaining a depositiontemperature at a constant value within a range of 400° C. to 500° C.,but said lower level metal film is formed by controlling a WF₆ flow rateon the order of 50 sccm to 100 sccm and said upper level metal film isformed by controlling a WF₆ flow rate on the order of 10 sccm to 50sccm.
 6. A method claimed in claim 1, wherein said lower level metalfilm and said upper level metal film are formed of tungsten by achemical vapor deposition while maintaining a WF₆ flow rate at aconstant value within a range of 10 sccm to 100 sccm, but said lowerlevel metal film is formed by controlling a deposition temperature onthe order of 400° C. to 450° C., and said upper level metal film isformed by controlling a deposition temperature on the order of 450° C.to 500° C.
 7. A method claimed in claim 1, wherein said lower levelmetal film is formed of tungsten by a chemical vapor deposition bycontrolling a deposition temperature on the order of 400° C. to 450° C.and by controlling a WF₆ flow rate on the order of 50 sccm to 100 sccm,and said upper level metal film is formed of tungsten by a chemicalvapor deposition by controlling a deposition temperature on the order of450° C. to 500° C. and by controlling a WF₆ flow rate on the order of 10sccm to 50 sccm.
 8. A method as recited in claim 7, wherein said firststep and said second step include forming respective layers ofconductive material by different processes whereby said second step isachieved by a process performed subsequent to said initial depositionprocess having excellent step coverage.
 9. A method as recited in claim8, wherein said different processes are performed by alteration ofprocess conditions during a continuous process.
 10. A method claimed inclaim 1, wherein said lower level metal film and said upper level metalfilm are continuously formed so as to control a stress of the whole ofsaid lower and upper level metal films by changing a film thicknessratio between said lower level metal film and said upper level metalfilm.
 11. A method as recited in claim 1, wherein an average internalstress of said lower level metal film and said upper level metal film isnot greater 8×10⁹ dyne/cm².
 12. A method as recited in claim 1, wherein:said lower level metal film is formed of a first tungsten film, saidupper level metal film is formed of a second tungsten film, and anaverage internal stress of said first and said second tungsten films isnot greater than 8×10 dyne/cm².
 13. A method as recited in claim 12,wherein said first tungsten film having an excellent step coverage has afilm thickness not smaller than 40% of a diameter of said contact hole,and a remainder of a desired thickness comprises said second tungstenfilm having the internal stress smaller than that of said first tungstenfilm.
 14. A method as recited in claim 12, wherein said first and saidsecond tungsten films are continuously formed.
 15. A method as recitedin claim 12, wherein: said first tungsten film is formed by a chemicalvapor deposition under a reaction rate controlling condition, and saidsecond tungsten film is formed by a chemical vapor deposition under asupply rate controlling condition.
 16. A method as recited in claim 12,wherein: said first and said second tungsten films are formed by achemical vapor deposition while maintaining a deposition temperature ata constant value within a range of 400° C. to 500° C., said firsttungsten film is formed by controlling a WF₆ flow rate on an order of 50sccm to 100 sccm, and said second tungsten film is formed by controllinga WF₆ flow rate on an order of 10 sccm to 50 sccm.
 17. A method asrecited in claim 12, wherein: said first and said second tungsten filmsare formed by a chemical vapor deposition while maintaining a WF₆ flowrate at a constant value within a range of 10 sccm to 100 sccm, saidfirst tungsten film is formed by controlling a deposition temperature onan order of 400° C. to 450° C., and said second tungsten film is formedby controlling a deposition temperature on an order of 450° C. to 500°C.
 18. A method as recited in claim 12, wherein: said first tungstenfilm is formed by a chemical vapor deposition by controlling adeposition temperature on the order of 400° C. to 450° C. and bycontrolling a WF₆ flow rate on an order of 50 sccm to 100 sccm, and saidsecond tungsten film is formed by a chemical vapor deposition bycontrolling a deposition temperature on the order of 450° C. to 500° C.and by controlling a WF₆ flow rate on an order of 10 sccm to 50 sccm.19. A method as recited in claim 12, wherein said first and secondtungsten films are continuously formed so as to control a stress of thewhole of said lower and second tungsten films by changing a filmthickness ratio between said first and second tungsten films.
 20. Amethod for forming a semiconductor device having a wiring conductor at asurface thereof, said method comprising steps of: forming a film ofconductive material at least initially by a process including adeposition process having excellent step coverage and having a firstlevel of stress in a first region of said film of conductive material,said first region extending over a first thickness of said film ofconductive material; developing a second level of stress less than saidfirst level of stress in a second region of said film of conductivematerial, said second region extending over a second thickness of saidfilm of conductive material; and patterning said film of conductivematerial to form a conductor.
 21. A method as recited in claim 20,wherein said step of forming a film includes respective steps of formingrespective layers of conductive material by different processes wherebysaid step of developing a second level of stress is achieved by aprocess performed subsequent to said initial deposition process havingexcellent step coverage.
 22. A method as recited in claim 21, whereinsaid different processes are performed by alteration of processconditions during a continuous process.
 23. A method as recited in claim20, wherein said step of developing a second level of stress includesion implantation in said second region of said film.
 24. A method asrecited in claim 23, wherein said step of developing a second level ofstress further includes heat treatment subsequent to said step of ionimplantation.
 25. A method as recited in claim 20, wherein said firstregion extends over a thickness of said film not smaller than 40% of adiameter of a contact hole in an insulator layer having said surface onwhich said film of conductive material is formed.
 26. A method asrecited in claim 20, wherein average stress in said film is determinedas a ratio of thicknesses of said first region and said second region.27. A method claimed in claim 26, wherein said average stress is notgreater than 8×10⁹ dyne/cm².
 28. A method claimed in claim 20, whereinsaid film of conductive material is formed of a tungsten film, and anaverage stress of said tungsten film is not greater than 8×10⁹ dyne/cm².29. A method as recited in claim 28, wherein said step of developing asecond level of stress includes ion implantation in said second regionof said film.
 30. A method as recited in claim 29, wherein said step ofdeveloping a second level of stress further includes heat treatmentsubsequent to said step of ion implantation.
 31. A method as recited inclaim 28, wherein said first region extends over a thickness of saidfilm not smaller than 40% of a diameter of a contact hole in aninsulator layer having said surface on which said film of conductivematerial is formed.
 32. A method as recited in claim 28, wherein averagestress in said film is determined as a ratio of thicknesses of saidfirst region and said second region.